1. Field of the Invention
The present invention relates to a reactor used for a vapor deposition scheme.
Recently, a technique of atomic layer deposition (hereinafter referred to as ‘ALD’) has been widely used as a vapor deposition method. For better understanding of the principle(s) of the present invention the following will explain about an ALD reactor as an exemplary prior art, but it should be noted that the present invention is not limited thereto.
2. Description of the Related Art
ALD injects, as shown in FIG. 1, one or more precursors into a reactor and carries out a purge/pump of the precursor to maintain or leave one or more molecule layers on a substrate. Then it injects one or more reactants into the reactor and carries out a purge/pump to obtain one or more mono-atomic reacted layers. Therefore, one or more mono-atomic layers are formed through one cycle consisting of four steps.
A conventional ALD reactor adopts a cross-flow scheme (this is also called as a ‘traveling-wave’ scheme) where a precursor, a reactant, a purge gas and the like are injected parallely to the surface of a target substrate for deposition, or a shower-head scheme where a precursor, a reactant, a purge gas and the like are injected perpendicularly to the surface of a target substrate for deposition. FIG. 2 illustrates a cross-flow ALD reactor, and FIG. 3 illustrates a shower-head ALD reactor.
In the cross-flow scheme precursors are injected parallely to the surface of a substrate as depicted in FIG. 2, so all the precursors do not necessarily reach the substrate at the same time, but a substrate near an injection port experiences an adsorption phenomenon first, followed by a substrate on the side of an exhaust port later on. Thus, adsorption can be expressed as a function of time. In particular, when large area substrates are used this phenomenon becomes more evident and it may even cause a serious problem, for example, compositions may vary or film properties may be changed according to the locations of an injection port and an exhaust port.
In the shower-head scheme, however, an injection port (sub-injection ports to be more specific) is spaced apart from a substrate by a uniform distance as depicted in FIG. 3, so precursors adsorb at the surface of the substrate almost at the same time. In this manner, the shower-head scheme, compared with the cross-flow scheme, can be advantageously used for obtaining a thin film having homogenous properties. Meanwhile, a reactor using such a shower-head injection port has a large volume so that it takes long to carry out a purge/pumping process and uses a large amount of precursors and reactants.
These two types of conventional ALD reactors periodically receive a precursor, a reactant, and a purge gas therein via a valve. Such a valve operates at high speed and at high frequencies. For instance, in order to deposit a 1 μm-atomic layer, the valve needs to operate 10,000 times or more for each process. This actually causes problems related to the lifespan of a valve. Moreover, both ALD reactors of the prior art are designed to be rather difficult for the application of remote plasma, the use of high frequencies including microwave, UV irradiation and so on.